In root canal procedures, the crown of a diseased tooth is opened so as to permit the canal to be cleaned and filled. A series of root canal instruments, each of increasing or decreasing diameter, are then used to enlarge, clean out, and smooth the walls of the root canal. These root canal instruments, also known as files, must be composed of a high strength, resilient metal capable of sufficient flexing for following the normal curvatures of the root canal. Each instrument has an elongate shank having a lower working length. Historically, dentists have used elongate, tapered endodontic files with the working length having helical cutting edges to remove the soft and hard material from within and adjacent the root canal area. However, the working length of the endodontic files can have a wide range of configurations such as helical or non-helical flutes, tapered or un-tapered working lengths, different shaped cross sections, and working lengths having varying pitch levels for the flutes.
Endodontic instruments as described above were conventionally fabricated by permanently twisting a stainless steel rod, and the angles formed between the surfaces would form the cutting edges which would spiral along the working length of the instrument. Machining processes were then developed wherein a cylindrical rod of stainless steel was moved past a rotating grinding wheel while the rod was slowly rotated.
As shown in FIG. 1A, in conventional machining apparatuses 1 utilizing the grinding method, the rod 12 is positioned to extend through a feed block 2 and an indexing block 3. The feed block 2 and indexing block 3 are then advanced manually or by using a system of cams and a series of gears so that the rod 12 axially moves past the rotating grinding wheel 4 in the X-coordinate direction. After the rod 12 is advanced past the rotating grinding wheel 4 a distance sufficient to form the first surface of the instrument, a table 5 supporting the components of the machining apparatus 1, including the feed block 2 and indexing block 3, is moved back to its original position along a path as depicted in the arrows below the apparatus 1. The rod 12 is thereafter indexed and again moved past the grinding wheel 4 to form the second surface of the instrument. The process of moving the supporting table 5 and indexing the rod 12 is repeated to form each subsequent surface of the instrument.
One problem associated with the conventional machining apparatuses used in the grinding method is the fact that the grinding wheel has to be movable to fabricate instruments of different configurations. For example, to fabricate instruments having a generally flat working surface, the grinding wheel has to be oriented to rotate about an axis generally parallel to the axis of the advancing rod. However, to fabricate an instrument having helical flutes of an arcuate configuration, the axis of the grinding wheel may be oriented so that the wheel lies in a plane which follows the desired helical configuration of the flutes. Furthermore, the grinding wheel has to be movable vertically to adjust the machining apparatus for fabrication of instruments having different diameters. The fact that the rotating grinding wheel is movable can cause a large amount of vibration of the rotating wheel, resulting in imprecise and faulty instruments. As a result, grinding wheels are often only operated at slower surface speeds in order to reduce vibration. Accordingly, there is a need for a machining apparatus having a fixed grinding wheel rotatable at a higher surface speed to fabricate endodontic instruments.
Another disadvantage of the conventional machining apparatuses used for the grinding method is that the instruments are fabricated in a time consuming, expensive, and imprecise manner. In some operations, after the rotating rod advances past the rotating grinding wheel to form the first surface, an operator has to manually change positioning of components of the machining apparatus and manually index the rod before advancing the rod past the rotating wheel to form the second surface. Manual operation of these steps leads to greater opportunities for human error, especially when indexing the small diameter rods to precise angle measurements. Additionally, conventional machining apparatuses cannot effectively advance the same working surface past the grinding wheel twice to fix cutting errors that occur during a single pass. This is due to the imprecision of the conventional machining apparatuses and their inability to start the rotating rod at the same angular position as was used during the working surface's first pass of the grinding wheel. Accordingly, there is a need for a machining apparatus and method which provides for improved automation and precise fabrication of endodontic instruments.
Yet another disadvantage is that these conventional machining apparatuses are limited in that each machine is often practically limited to manufacturing a single instrument configuration. It was found to be very time consuming and difficult to precisely adjust the positioning of components, change operating parameters, and recalibrate the machine, the adjustments typically being done manually, to switch from producing an instrument of one configuration to an instrument of a second configuration. For example, for instruments having a nontapered working length, the axis of the index block may be horizontal with respect to the axis of the grinding wheel. However, if the instrument has a tapered working length, the axis of the index block may be slightly inclined with respect to the rotational axis of the wheel. Thus, it was found that using multiple conventional machining apparatuses, one for each type of desired configuration, was more advantageous than having to adjust the settings. As files of different diameters, shank lengths, angles of tapering, dimensions of flutes, variety of cross sections, etc. are used in root canal procedures, many different machines were needed to fabricate the various endodontic instruments. Accordingly, there is a need for one machining apparatus that can be utilized to fabricate a variety of instruments that have various dimensions and surface features.